The present invention relates to a magnetic disc apparatus or the like using an electric filter for waveform equalization of a read signal and, more particularly, to a magnetic disc apparatus for executing writing and reading operations by controlling so as to set the optimum parameter for every head.
In recent small disc apparatuses, the realization of a large capacity and a high density is further demanded in association with the realization of a small size and a high performance of a computer system.
For this purpose, it is necessary to further properly set a low pass filter, a waveform equalizing circuit, and a pulse detection level other than the conventional apparatus with respect to physical characteristics of a magnetic head and a magnetic disc medium, a recording position on the medium, and a recording frequency.
In the conventional magnetic disc apparatus, proper circuit characterisitics of a read pass filter and a waveform equalizing circuit and a proper value of a pulse detection level which is used to detect the peak of a read signal differ depending on a difference of a combination of the magnetic head and the magnetic disc medium or the like.
The circuit characteristics of the read pass filter and waveform equalizing circuit and the pulse detection level are switched in accordance with the cylinder position at which the magnetic head is located (the radius position of the magnetic head from the center of the medium).
As circuit characteristics and the peak detection level which are used in the above switching operations, hitherto, the values obtained by a statistic method are used in many cases.
When the set values to decide the characteristics of the read pass filter and waveform equalizing circuit and the pulse detection level which were obtained by using the statistic method are used, however, the result of judgment regarding whether a combination of a certain magnetic head and a certain magnetic disc medium can effectively read out the data by the set values which were switched in accordance with the cylinder position or not is given by only a statistical probability, so that the optimum values cannot be always set.
On the other hand, the set tolerances of the characteristics of the low pass filter and waveform equalizing circuit and of the pulse detection level are further narrow due to the realization of a high density. Furthermore, in case of increasing the number of magnetic disc media and the number of magnetic heads in order to increase the capacity of the magnetic disc, a probability such that all of the magnetic heads can effectively read out the data on the basis of the set values which were statistically obtained further decreases.
There are, consequently, problems such that not only the yield of the apparatus deteriorates but also there is a case where the set values are set the values which are as close as the limit values of the tolerances in dependence on the magnetic head, and the stability and reliability of the whole apparatus deteriorate.